Hand print, thermogram footage. Thermography records the temperature of surfaces by detecting long-wavelength infrared radiation. The colours show variations in temperature. The scale runs from white (warmest), through yellow, orange, red and purple to blue (coldest). This footage shows a human hand radiating heat (yellow) placed on a cool surface (black). The heat transfers from the hand to the surface, leaving a 'heat print' behind when the hand is removed. This fades as the surface cools.